Cover Crop Interseeder and Applicator

The Penn State Cover Crop Interseeder and Applicator was designed to help establish cover crops in areas where cover crop establishment is not that feasible because of a late harvest and short season.
Cover Crop Interseeder and Applicator - Articles

Updated: August 8, 2017

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Cover Crop Interseeder and Applicator

With this system, cover crops are interseeded early in the season but provide minimal competition to the corn. The interseeder is designed to be able to apply sidedress N fertilizer and a postemergent herbicide while seeding the cover crop, eliminating the need for additional trips across the field and reducing the cost of seeding the cover crop. Read our notes below for more on the benefits of cover crops and the rationale behind the concept of interseeding.

Cover crops can play many important roles in cropping systems that are well recognized: preventing soil erosion, enhancing soil carbon, reducing drought stress, suppressing weeds, minimizing nutrient runoff and providing supplemental forage. Despite these advantages, the establishment of cover crops is often limited by the late fall harvest of the corn or other crops, which leaves little growing season for a functional cover crop to become established. The cost of cover crop seeding can also be an issue with the expense of an added trip across the field and seed costs keeping some crop producers from using the practice.

With increasing needs to limit nutrient runoff and leaching into the Chesapeake Bay watershed, a growing desire to harvest corn stover, and an increasing need to develop strategies for increasing forage production on livestock farms, there is a critical need to develop technologies that overcome the issues with cover crop establishment in corn in our region.


With the development of the new machine, interseeding has considerable potential to help continue to improve the sustainability of corn production by promoting cover crops, sidedress N applications, post emergent herbicide applications, and no-till crop production while reducing runoff. It could also increase the productivity of our crop production systems by allowing us to utilize more of the stover or by producing forages on some of the land dedicated to corn grain production. Many issues remain to be evaluated to maximize the potential of this system, however. In the future, it will be necessary to carefully evaluate these issues as this technology is developed.

Support for these demonstrations and publications were provided by Capital Resource Conservation and Development Area Council with funding from the Pennsylvania Department of Environmental Protection.

Prepared by: Greg W. Roth, William S. Curran, Corey Dillon, Christian Houser and W.S Harkcom, Department of Plant Science

Figure 1. Interseeder seeding between rows of corn.

The interseeder helps no till farmers to relay crop and make it possible for farmers to have healthy year round soil and be environmentally friendly.

There are several benefits of relay cropping. It ensures cover crop, captures nutrients in the soil, reduces surplus nitrogen, reduces runoff in the winter, protects soil from wind and water erosion, can become a natural fertilizer, saves harvesting time, and left over cover crops can double as forages for farm animals and wild deer.

No Tillage Production

Modern corn production tactics are being adopted to help mitigate the impact of corn and soy production on soil and water resources. One of these tactics is no till production, which involves not plowing or cultivating between crops in the fields. This method reduces the potential for soil erosion, conserves soil moisture, and reduces the energy associated with corn production.

Benefits of Having Cover Crops

Figure 2. Roots of inter seeded clovers after harvest.

The establishment of cover crops following harvest has been promoted to minimize runoff and plant nutrient losses from either residual amounts of fertilizer or from animal manure applications made to the field following harvest. The growth of cover crops is often limited by the late fall harvest of the corn crop in some areas, which leaves little growing season for crops such as clover or rye-grass to become established. This method of combining the three operations (spraying, fertilizing and seeding a cover crop) and performing them in a no-till field is novel and will reduce the cost and energy associated with multiple trips while facilitating these environmentally sound sound practices. The method also facilitates the establishment of cover crops in regions where the growing season is too short or the corn harvest is too late in the fall to allow for successful establishment of cover crop following harvest.

The Interseeder

The interseeder utilizes strip or zone tillage technology between corn rows to prepare a 16 inch wide seedbed between each row, broadcasts the cover crop seed across this area, and then incorporates the seed and packs the soil with a packing assembly. At the same time, a post-emergent herbicide is applied to the field for weed control and a liquid nitrogen fertilizer application is strategically directed just off the side of the corn row to maximize the effectiveness.

Currently, the most widely used method for farms to increase crop yield is to till and utilize significant amounts of chemical fertilizer and herbicides. This technique, while good for crop yield is detrimental to soil quality and the local environment. The interseeder is positioned to become a standard for farmers located along the Mid-West, Mid-Atlantic and Great Lakes regions. The main drivers for using this technology is to: 1) naturally improving soil quality; 2) it helps farm operations be more compliant with regulations; and 3) saves money for farmers. The apparatus can be attached to most existing tractors and can be built from 4 rows to 12 rows.

Previous studies have demonstrated that interseeded cover crops or “relay crops” could have some potential for establishment of cover crops without impacting the yield and growth of the primary crop.

Researchers from Cornell (Scott et al., 1987) have reported successfully seeding cover crops during the late spring in fields that were tilled with minimal residue on the soil surface with no impact on crop yields. They determined that annual ryegrass and red clover were the most effective of several cover crop species evaluated. In this system, cover crop seeds were broadcast on the soil surface and incorporated using a row crop cultivator.

A second study showed that this system could be used in soybean production as well (Hively and Cox, 2001). Canadian researchers have reported the effective use of seeding devices that can establish cover crops in a standing crop of corn in a tilled seedbed (Walters, 2004) however this machine is not adequate for use in no-till systems. Their experience and others in Europe, however, has demonstrated the potential utility of this in season cover crop or "relay crop" system as a part of corn production.

In New York, a more recent study by Kleinman et al. (2005) showed that establishing a red clover or ryegrass cover crop at planting showed great potential for reducing non point P runoff from corn fields, but the ryegrass seeded at planting tended to reduce corn yields. By delaying ryegrass planting, it may be possible to avoid this yield depression.

Interseeding cover crops in corn is a promising management practice that could improve the adoption of cover crops where they have not been feasible before. As with any new practice, to improve the odds of success, some attention to management is necessary. In this factsheet, we share some of the practices that can improve the potential of interseeding cover crops based on our work and the observations in the literature.

Field Selection

Successful interseeding is a function of the relationship of the cover crop to the corn crop and its management. The ideal management probably varies a bit from region to region and field to field. The competitiveness of the corn crop and the degree of heat and drought stress in a region will impact the potential for success, fall biomass accumulation and potential interseeding management.

Our general recommendation is to target interseeding at the V5 to V7 stage of corn. At this stage, the potential for injury from short residual preemergence herbicides is reduced and the timing is good for sidedress N. Postemergent glyphosate or glufosinate (Liberty) could also be applied at this time if necessary to control escaped weeds prior to cover crop emergence. In most areas, we have been successful with this approach and have achieved respectable cover crop establishment. The amount of cover crop biomass accumulation in the fall will depend on a number of factors including cover crop species, corn hybrid maturity as well as planting and harvest dates, corn grain vs. silage, and soil fertility management.

The success of interseeding in our work and in others have shown that factors such as plant population, timing of interseeding and hybrid maturity can affect the successful establishment and cover crop growth in the fall. These factors should be adjusted if need be, to improve interseeding success in a particular area.

We have had reasonable success with corn populations up to 32,000 per acre with our typical recommendations. Others have found that reducing plant populations to 22,000 to 26,000 will improve establishment and increase the fall cover crop biomass. However, in most cases we don't want to be reducing corn populations to the extent that we will be impacting yield or profitability. Using hybrids or targeting fields where moderate corn populations would work is one management strategy to consider.

Earlier interseeding from V3-V5 has been successful in Canada and has increased establishment and cover crop biomass in the fall. This may be necessary in environments where the corn crop is too competitive for later interseeding. We have not evaluated interseeding prior to V5 corn and do have some concern for potential cover crop competition with corn. We suggest doing some experimentation on your farm in smaller fields or plots and testing which tactics work best for you. We have had some success with interseedings at later stages such as V8 but these are best targeted to fields with less competitive corn.

In more competitive environments, there could be benefit for earlier maturity hybrids. Often, these are shorter statured with earlier dry down and harvest. This will allow better light penetration in early fall and promote cover crop growth and development. Changes in hybrid maturity should be considered only if they are part of a whole farm management plan and not if they impact profitability. Often reduced drying costs, earlier harvest, improved prices and residual effects of cover cropping can offset modest yield penalties associated with earlier hybrids.

Cover Crop Interseeder Herbicide/Weed Management Guidelines

Interseeding cover crops will impact the weed management strategies in a field since some herbicides can impact the establishment of the cover crops. Fields with lots of weeds or with certain herbicide resistant weeds may not be good candidates for interseeding as these may require longer residual herbicides or multiple postemergence applications.

Over the last five years, we have evaluated some residual broadleaf and grass herbicides in corn for use with interseeding. The following information is based on these observations and lists our current recommendations for some herbicides that 1.) Will likely be a problem; 2.) Some that can be problematic particularly at full rates; and 3.) Some that are compatible with interseeded cover crops. Our goal is to provide recommendations that carry minimal risk for cover crop herbicide injury.

Our basic approach with herbicides and interseeding has been to use a no or short residual burndown herbicide or tillage followed by a glyphosate or glufosinate (Liberty) application prior to interseeding. The ability to use residual herbicides is a function of the type of cover crop being interseeded. When interseeding multiple species that include grasses, legumes, and Brassicas such as forage radish, then residual herbicide options are fewer. Single species cover crop (e.g. grass or legume) can allow greater herbicide choice (Table 1).

For corn that is not Roundup Ready or Liberty Link, similar preemergence programs can be used, but POST herbicide options do not include glyphosate or Liberty. The herbicides listed in Table 2 have limited residual activity and/or tolerance to grasses, legumes or Brassica species. These foliar herbicides must be applied prior to interseeding when weeds are small. This will generally be 3 to 5 weeks after corn planting and a week or more prior to interseeding. In organic systems, a combination of tillage and cultivation is used for weed control and herbicide impacts on cover crops are not a concern. If grazing of the cover crop is planned, most corn herbicides allow grazing of corn stalks although there is nothing on the herbicide labels concerning interseeded cover crops. Table 2.2-18 in the 2015/16 Penn State Agronomy Guide lists herbicide grazing restrictions for corn.

We have had limited experience and less success interseeding in soybean. Full-season soybean is very competitive and it is difficult for interseeded cover crops to survive the intense shading when soybeans develop a closed canopy. Planting shorter-season varieties that are not as tall, planting soybeans a little later in the season such as in June or as double-crop soybean after a winter cereal in regions where this is common can allow for greater interseeding success. Residual soybean herbicides present the same concern for the success of the cover crop as corn herbicides. We have not tested residual soybean herbicides and interseeded cover crops, but provide the following guidelines based on our herbicide experience (Table 3).

Species selection

The ideal species for interseeding are those that are cool season, somewhat drought and shade tolerant and relatively easy to establish. These have mostly included annual ryegrass, and red and crimson clovers (See Table 4).

Annual ryegrasses are available as true annuals or Italian ryegrasses. The annual ryegrass are less expensive, and sometimes produce a bit more biomass, but they can head out in the fall and are more subject to winterkill. The Italian ryegrasses don't head out and often have superior winter hardiness. Most of our research has utilized annual ryegrass and we have less experience with Italian ryegrass. We suggest seeding ryegrass at 15 to 20 pounds per acre as a single species or 10-15 pounds per acre in a mix with clover.

Of the clovers, medium red clover has been the most successful in our research. It is fairly shade tolerant, has good winter hardiness and is less expensive than some other clovers. Be sure to properly inoculate legumes. Seed medium red clover at 8 to 10 pounds per acre as a single species or 5-8 pounds per acre in a mix with ryegrass.

An alternative to medium red clover is crimson clover. It often produces a bit more biomass in the fall after interseeding, but is subject to winterkill in Pennsylvania and North. Seed crimson clover at rates of 10-15 pounds per acre as a single species or 8-12 pounds per acre in a mix with ryegrass.

We have evaluated orchardgrass, Kentucky bluegrass, perennial ryegrass, tall fescue, and several other legumes such as hairy vetch, ladino clover, and yellow blossom sweet clover. Orchardgrass has worked fairly well and is more winter hardy than the ryegrass, while the other grasses have not been successful. We have had mixed results with hairy vetch and the other clovers have not been successful.

Table 1. The likelihood of herbicide injury to grasses, legumes, brassica species or mixtures when inter-seeded 5 to 7 weeks after corn planting. Injury likely indicates these herbicides should not be used when interseeding sensitive cover crop species. Injury possible indicates that there is potential to use these herbicides, but some injury may occur. Use these herbicides as setup programs (1/2 - 2/3X) prior to post herbicides. Herbicides in the Injury unlikely category can be used at normal (1X) rates and should allow safe establishment of specified cover crop species. This table does not list all products that contain these active ingredients.

Cover Crop - Grass

Injury Likely

Active Ingredient
Key Products
atrazine (>1lb)Atrazine, others
nicosulfuronAccent, Steadfast
pyroxasulfoneZidua, Anthem

Injury possible

Active Ingredient
Key Products
acetochlorHarness, Degree
atrazine (<1 lb)Atrazine
isoxaflutoleBalance, Corvus

Injury unlikely

Active IngredientKey Products
clopyralidStinger, Hornet
flumetsulamPython, Hornet
rimsulfuronResolve, Basis

Cover Crop - Legume

Injury Likely

Active Ingredient
Key Products
atrazine (>1lb)Atrazine, others
clopyralidStinger, Hornet
FlumetsulamPython, Hornet
pyoxasulfoneZidua, Anthem

Injury possible

Active Ingredient
Key Products
acetochlorHarness, Degree
atrazine (<1 lb)Atrazine
dicamba (PRE)

Injury unlikely

Active IngredientKey Products
rimsulfuronResolve, Basis

Cover Crop - Brassica

Injury Likely

Active Ingredient
Key Products
atrazine (>1lb)Atrazine
FlumetsulamPython, Hornet

Injury possible

Active Ingredient
Key Products
atrazine (<1 lb)Atrazine
pyroxasulfuoneZidua, Anthem

Injury unlikely

Active IngredientKey Products
acetochlorHarness, Degree
Stinger, Hornet
dicamba (PRE)
s-metolachlorDual, others

Cover Crop - Grass/ legume/ Brassica mix

Injury Likely

Active Ingredient
Key Products
atrazine (>1lb)Atrazine
s-metolachlorDual, others

Injury possible

Active Ingredient
Key Products
acetochlorHarness, Degree
atrazine (<1 lb)Atrazine
Dicamba (PRE)

Injury unlikely

Active IngredientKey Products
rimsulfuronResolve, Basis
Table 2. Postemergence corn herbicides that have short residual activity or cover crop tolerance. Herbicides must be applied prior to interseeding cover crops
Tolerant cover cropsActive ingredientTrade name
Grassesflumetsulam + clopyralidHornet
GrassesglyphosateRoundup or other glyphosates
Grasseshalosulfuron + dicambaYukon
Grassesrimsulfuron + thifensulfuronResolve Q
Legumes or Brassica speciesbentazonBasagran
Legumes or Brassica speciesbromoxynilBuctril
Legumes or Brassica speciescarfentrazoneAim
Legumes or Brassica speciesfluthiacetCadet
Legumes or Brassica speciesglufosinateLiberty
Legumes or Brassica speciesglyphosateRoundup or other glyphosates
Legumes or Brassica speciesthifensulfuronHarmony
Grasses + Legumes or Brassica speciesbentazonBasagran
Grasses + Legumes or Brassica speciesbromoxynilBuctril
Grasses + Legumes or Brassica speciescarfentrazoneAim
Grasses + Legumes or Brassica speciesfluthiacetCadet
Grasses + Legumes or Brassica speciesglufosinateLiberty
Grasses + Legumes or Brassica speciesglyphosateRoundup or other glyphosates
Grasses + Legumes or Brassica speciesthifensulfuronHarmony
Table 3. Suitability of residual soybean herbicides for interseeded cover crops. Herbicides must be applied prior to cover crop interseeding.
Active ingredientTrade namesGrassesLegumesBrassica species
chlorimuronClassic, Canopy, Envive, etc.OKNoNo
fomesafenFlexstar, ReflexOKNoNo
quizalofopAssure, TargaNoOKOK
Table 4. Suggested seeding rates for interseeding cover crops on a per acre basis. These are the species we have experience with. Other species may also be suitable, but we have not tested them.
Seeding TypeSpeciesPounds/acre
Single SpeciesAnnual ryegrass15-20
Single SpeciesOther grasses (e.g. orchardgrass)15-20
Single SpeciesMedium red clover8-10
Single SpeciesCrimson clover10-15
Single SpeciesDaikon radish5
In MixturesAnnual ryegrass10-15
In MixturesMedium red clover5-8
In MixturesCrimson clover8-12
In MixturesDaikon radish3-5

Another species we have evaluated is forage or Daikon radish. Seeding rates of 3 to 5 pounds with ryegrass have been effective. The radish will not produce the large roots in the interseeded crop situation but can produce some biomass and taproots to complement the grass.

Often mixtures of the clovers and ryegrass do well and radish can be added to the mix. Mixtures provide diversity and the potential benefits that come along with multiple species. A typical ryegrass /clover/radish mixture would include about 12 pounds of ryegrass, 8 pounds of red clover and 3 pounds radish. We are using a mixture of annual ryegrass (10 lb) and orchardgrass (10 lb), radish (3 lb), plus or minus a red or crimson clover (5 lb) in some trials.


In general we have fertilized interseeded corn crops similarly to other corn crops. Concentrated applications of UAN dribbled over cover crop rows could cause some cover crop seedling mortality or stimulate the cover crops in some cases. Side dressing between every other row could exacerbate these effects and result in heavy cover crop growth in every other row, especially in a less competitive corn crop. Side dressing with the interseeder machine or another apparatus that could apply the N near the base of the corn plants could minimize these effects.

Harvesting Impacts

The silage harvest process can damage the interseeded cover crop but often it will quickly recover and within two weeks with good growing conditions, it should look good again. If conditions are wet at harvest with soil compaction from large trucks and choppers, some permanent damage can occur. When harvesting for grain, try to avoid tactics that would smother the cover crop. Operate the combine a bit higher to avoid shredding the stalks, while still harvesting the grain. Avoid mowing the corn stalks after harvest as this could smother the cover crop with corn stover. Instead consider leaving a high stubble in the field to reduce the stover on top of the cover crop.

Cover Crop Termination

Most cover crops are fairly easy to control in a burndown program as long as you pay attention to detail. There are a few species that may require special consideration. In general, most programs begin with glyphosate, which tends to be more consistent than paraquat (Gramoxone). Liberty has a narrow fit, mostly for horseweed/marestail control, but does not add much for cover crops. Herbicide effectiveness ratings for some common cover crops are provided in Table 5. Here are some considerations as you get into the field this year.

Guidelines for glyphosate. All cover crops should be actively growing and capable of intercepting the herbicide spray (e.g. not covered with crop residue). Remember to use a sufficient rate, which generally ranges from 0.75 lb ae to 1.5 lb ae/acre. The 22 fl. oz rate of Roundup or 32 fl. oz rate of Credit, Rascal, Clearout, etc. = 0.75 lb. In general, application alone in good quality water along with appropriate adjuvants (surfactant + AMS) is best and reducing the carrier volume to 10 gal/acre can increase activity. Do not add 28 or 32% UAN or other fluid fertilizers to the spray tank. If the water source has a high pH (8 or greater), consider adding an acidifying agent to the spray solution. Avoid tank mixing with higher-rate (> 0.25 lb) clay-based herbicides (WDG, WG, DF, DG, F) like atrazine, simazine, and metribuzin. Other herbicides such as 2,4-D, dicamba, clopyralid, Balance or Corvus, Resolve or Basis Blend, etc. are OK.

Annual ryegrass

Annual ryegrass continues to be somewhat challenging to control. Glyphosate is the preferred herbicide and paraquat (Gramoxone) does not provide consistent control. Application during sunny warm days is best and cloudy weather will slow activity. Under cool conditions, it may take 2 to 3 weeks to kill the ryegrass and a second application may be necessary. Previous research suggests that small ryegrass is easier to control, but mild air temperatures 1 to 2 days before, during, and 1 to 2 days after application are likely more important. Apply glyphosate at 1.25 to 1.5 lb ae/acre following the guidelines provided previously.

Hairy vetch, red clover, and crimson clover

For control of clover or other legume cover crops, glyphosate alone will not kill most legumes, but it is useful in mixture with other herbicides. Gramoxone alone is also not very effective on legumes and should be mixed with atrazine or metribuzin for increased performance. Dicamba (Banvel/Clarity) is one of the best herbicides for control of legume cover crops. It is often a necessary tank-mix partner with glyphosate for control of red or white clover. A 2,4-D ester formulation will effectively control hairy vetch and field peas. I am less familiar with crimson clover control and unsure if 2,4-D is adequate or dicamba is necessary. Both 2,4-D ester and dicamba can be tank-mixed with glyphosate without loss in activity and can be used in corn. Use a minimum of 12 fl. oz/acre of Banvel or Clarity or 2,4-D ester tank-mixed with glyphosate. For corn, apply dicamba or 2,4-D ester 7 to 14 days before planting or 3 to 5 days after planting for greater crop safety and plant corn at least 1.5 inches deep. Clopyralid is also effective on legumes and is a component of several corn herbicides. Dicamba and clopyralid are not suitable for soybean and 2,4-D ester (1 pt) must be applied at least 7 days ahead of soybean planting. Clopyralid can persist up to 12 months and injure legumes.

Nutrient Requirements of Succeeding Crop

We are still working to develop recommendations for corn following an interseeded crop. There should be some effect on the N requirement for corn following a well-established clover or clover grass cover crop. Following clover interseeded into wheat, this is often about 50 pounds per acre. Following a ryegrass crop, there could be some benefit if the grass was manured over the winter. Our recommendation in the Penn State Agronomy Guide is to increase the N contribution from an overwinter manure application from 20% of the manure N without a cover crop to 45% contribution with a cover crop not harvested for forage.

Without a manured cover crop, there is potential for some N immobilization from a grass cover crop like ryegrass and in this case, there may not be much N contribution from the cover crop to the succeeding corn crop. In the longer term, ryegrass should improve soil organic matter and reduce the need for N. In the short term, it may be good to maintain current N rates and also strive for some N at planting to offset any potential immobilization issues.

Table 5. Effectiveness of herbicides for control of common cover crops (based on Penn State research or our best guess). Control ratings: 10 = 95-100%; 9 = 85-95%; 8 = 75-85%; 7 = 65-75%; 6 = 55-65%; and N = less than 55%.
Rate* (lb/acre)Annual ryegrassWinter ryeWinter wheatCrimson cloverRed cloverWhite cloverHairy vetch
2,4-D ester0.5NNN7+869
2,4-D ester1NNN89710
Glyphosate +2,4-D ester0.75 + 0.58998+8810
Glyphosate +dicamba0.75 + 0.58998+9910
Paraquat + Atrazine or Metribuzin0.5 + 1 or 0.2578+8+98+79

*0.75 lb Glyphosate = 32 fl. oz of a 41% glyphosate; 0.5 lb paraquat = 2 pt Gramoxone SL; Clopyralid is a component of Stinger, Hornet, and Surestart/Tripleflex.


Prepared by Greg Roth, Bill Curran, John Wallace, Department of Plant Science, Penn State University, Matthew Ryan, Soil and Crop Sciences Section, Cornell University and Steven Mirsky, Sustainable Ag Systems Laboratory, USDA-ARS (5/8/2015).

There is some concern about the impact of the cover crop on the corn. In most cases, though, we have observed that the corn is very competitive with the cover crop.

The concept is to seed the cover crop so that establishment occurs following the "weed free" period (6-7 weeks after planting) so that any impact on the corn is minimal, provide weed control treatments at interseeding and use cool season cover crops that are not as competitive as warm season weed species. We are currently conducting a multistate trial with interseeded cover crops in NY, PA, VT and MD to further assess yield impacts of interseeded crops in our region.

Figure 1. Impact of interseeding different species at V6 on corn grain yields at Rock Springs in 2013.

Our initial results are supporting the concept that yield impacts are minimal. In our 2013 trial at Rock Springs where we got good establishment early of several species, the impacts on corn yield were negligible (Figure 1). We are conducting these studies across a range of environments to better understand the relationship between interseeding and grain yield. Our hope is that any yield impacts in the year of interseeding would be offset by higher yields, better soil quality and less fertilizer use in subsequent years.

A number of published studies have evaluated interseeding in the literature and have generally found no impact on corn yield with plantings at the V4 to V7 stages of growth, or 4 to 7 fully exposed leaves. A Cornell study concluded that intercrops of red clover, ryegrass and other species had no impact on corn yields when the interseeding was done at the 6 to 12 inch tall corn stage (Scott et al, 1987). Michigan State study (Baributsa et al., 2008) found that interseeding red clover or chickling vetch in corn over four years had no impacts on corn yields and that the clover could provide N to a succeeding crop.

Canadian studies have found similar conclusions. In Ontario, a two year study concluded that intercropping corn with red clover could provide soil protection without impacting silage corn yields (Wall et al., 1991). In Quebec, Carruthers et al. (2000) also showed that intercropping with forages seeded 3 weeks after corn planting did not impact corn yields and concluded "The ability toproduce silage equal in yield to monocrop corn at a reduced cost and risk of environmental damage makes this an attractive intercropping system for eastern Canada". In British Columbia, relay cropping with ryegrass planted at the 3 to 6 leaf stage is an accepted practice described in an advanced production manual for corn silage (Bittman and Schmidt, 2004). They note that planting ryegrass before the 3 leaf stage may suppress corn growth. Relay cropping in that region has been shown to dramatically reduce runoff from manured silage corn fields (van Vliet, 2002).

South American studies are also evaluating intercropping and have found similar results. One recent example of the studies there is that Borghi et al. (2013) concluded that Intercropping systems with corn and guineagrass did not reduce the corn grain yield compared with sole corn crops.

This is not an exhaustive list of the literature on the topic of yield impacts of interseeded crops, but provides a sampling of the evidence that cover crops can be intereseeded in corn with minimal impacts on yield in the year of intereseeding.

However, as with the introduction of any new technology, there will likely be some new concepts learned about this system and continuing improvements in management. In the introduction of no-till corn for example, weed control, soil compaction and planting issues often reduced yields in initial work, but eventually these were overcome with improved management to reap the benefits of no-till crop production. Our goal is that we can achieve the same with the concept of interseeding cover crops.


Baributsa, D.N., E.F.F. Foster, K.D. Thelen, A.N. Kravchenko, D.R. Mutch, and M. Ngouajio. 2008. Corn and cover crop response to corn density in an interseeding system. Agron. J. 100:981-987. doi:10.2134/agronj2007.0110

Bittman, S. and O. Schmidt. 2004. A recipe for relay cropping. In Advanced Silage Corn Management: A production guide for coastal British Columbia and the Pacific Northwest. Bittman, S. and C.G. Kowalenko, ed. Pacific Field Corn Association, Agassiz, BC.

Borghi, E., C.A. C. Crusicol, G. P. Mateus, A.S. Nascente, and P.O. Martins. 2013. Intercropping time of corn and palisadegrass or guineagrass affecting grain yield and forage production. Crop Sci. 53:629-636.

Carruthers, K, B. Prithiviraj, Q. Fe, D. Cloutier, R.C. Martin, and D.L. Smith. 2000. Intercropping of corn with soybean, lupin, and forages: silage yield and quality. Journal of Agronomy and Crop Sci. 185:177-185.

Dickey, J.B.R. 1947. Efficient corn growing. Pennsylvania State College, Agriculture Extension Service, Circular 305.

Scott, T.W., J. Mt. Pleasant, R.F. Burt, and D.J. Otis. 1987. Contributions of ground cover, dry matter, and nitrogen from intercrops and cover crops in a corn polyculture system. Agron. J. 79:792-798.

van Vliet, L. J. P., B.J. Zebarth and G. Derksen. 2002. Effect of fall-applied manure practices on runoff, sediment, and nutrient surface transport from silage corn in south coastal British Columbia.Can. J. Soil Sci. 82: 445-456.

Wall, G.J., E.A. Pringle and R.W. Sheard. 1991. Intercropping red clover with silage corn for soil erosion control. Can. J. Soil Sci. 71: 137-145.

Drs. Roth and Curran have a financial interest in Interseeder Technologies, LLC, the company which licenses the Interseeder from The Pennsylvania State University. These relationships have been reviewed by the University's Individual Conflict of Interest Committee and are currently being managed by the University.

Prepared by Greg W. Roth, and William S. Curran Department of Plant Science, Penn State

Figure 2. Interseeded clover during midsummer under the corn canopy.

Our goal with the design of the interseeder was to develop an affordable machine that could do the interseeding effectively as well as improve the application of the fertilizer and herbicide.

To address this issue, we developed a machine in conjunction with Penn State Agronomy Research Farm to facilitate interseeding in no-till and reduced tillage corn crops. The machine uses coulter tillage in the row to prepare a shallow seedbed followed by packing wheels and a drag chain to incorporate the seed. Since interseeding often coincides with sidedressing and postemergent herbicide applications, we added the capability of applying N fertilizer next to the corn row and applying herbicide to the machine.

In 2010, we initiated several studies evaluating the potential of interseeding cover crops in corn using the newly developed machine. Our initial studies with interseeding cover crops have been positive. We established two studies to evaluate the potential of seeding several cover crop species at sidedressing (V7 growth stage of corn). We were able to successfully establish ryegrass, red clover, white clover and a red clover/ryegrass mixture in no-till corn following both corn and soybeans. There was no significant impact on yield. Since the establishment of the crop is after the "critical weed free period" in corn, the expected impacts on yield are likely to be small. Future studies will attempt to duplicate these results and will assess the impact of the cover crops on subsequent crop yields.

Figure 3. Interseeded ryegrass/clover cover crop growth in April that could be grazed.

Characteristics of the ideal interseeding species may be different that those for more traditional cover crops. Species or varieties that can emerge with minimal moisture, can tolerate the heat and shade in these environments, and can provide good fall growth and winter cover are ideal. Also refining the ideal seeding rates for this system in our environment is also critical. Lower seeding rates could reduce the cost associated with the cover cropping system and also allow for inclusion of more species in the cover crop mix if desired. Earlier seeding dates could have more potential in shorter season environments or in fields where fall grazing and forage production has some potential.

Another timely potential benefit is the potential for improved nutrient recycling. There should be potential for improving the nutrient retention of mobile nutrients such as N, S and even P and K, as noted in some previous research. Grasses are vigorous competitors for soil K and could help to extract soil K for use by subsequent crops. Interseeded legumes could fix nitrogen, which could be used by subsequent crops.

The potential of fall grazing corn stalks is another application that could be attractive to some producers. A ryegrass or ryegrass/clover cover crop could provide a nice complement to grazing corn stalks for beef or sheep animals. Grazing could be done in the fall or early spring. It may be necessary to fertilize the cover crop late in the summer to maximize the potential dry matter production in this system.

Figure 4. Planting corn in an interseeded corn stubble field.

An interseeded cover crop could be especially useful where corn stalks are removed for bedding or other uses. In these fields, removal of carbon in the stalks can be an issue and could eventually lead to lower soil organic matter levels. Soil erosion can also be an issue on these fields unless a cover crop is established, which is difficult in northern counties. An interseeded cover crop could help to alleviate both of these issues.

Finally, an interseeding may also be able to minimize the potential yield impact of growing corn following corn, which is common in Pennsylvania. In interseeded fields, second year corn could be planted into a legume grass mix, for example, which is a much different environment than corn stubble. If the interseeding is done only in row middles, then the second year of corn can be planted next to the original corn rows and avoid the problem of planting into a dense cover crop.

Another interesting issue is the potential impact of the cover crops on the development of weed species in corn fields. It is likely that a vigorous interseeded cover crop could minimize the development of some late emerging winter annual weed species that are becoming a problem in row crops. A Canadian group, Abdin et al. (2000), indicated that interseeded cover crops complemented cultivation in providing weed control in corn.

Several challenges exist to maximize the potential of interseeding cover crops. One issue related to interseeding is the impact of the preemergent herbicide application on the establishment of the cover crop approximately 6 weeks later. We have initiated a study to assess the impacts of various common herbicides on the establishment of the ryegrass, red clover, and white clover seeded at sidedressing. Our initial results were encouraging with successful establishment under most of the herbicide regimes. More evaluation of this issue is necessary before we can make recommendations. It may be that a reduced rate preemergence program followed by a non selective glyphosate or glufosinate application at sidedress may be the optimum solution.

Another weed management issue is the termination of the cover crop. One of the most successful cover crops, ryegrass, can be difficult, but not impossible to kill in the spring. Careful attention to glyphosate rates is necessary to effectively terminate the crop.

Interseeding would also be an additional cost to the producer, but if the seeding could be combined with another trip across the field, then this cost could minimized. And if the potential benefits can be documented from nutrient savings, increased yield of corn on corn, additional revenue from stover or forage, and decreased runoff and leaching, then cost of establishment will be less of an issue.

2013 Ryegrass at Corn Harvest in Rock Springs

2013 was an exciting year for the Penn State Cover Crop Interseeder Team. We made modifications to our design which turned out to be quite successful.

We launched our USDA NRCS CIG project in conjunction with Cornell and USDA-ARS designed to document yield impacts and potential nutrient savings to subsequent corn crops. We expanded our trials from northern Vermont to Maryland and we were able to test the interseeder under a wide range of conditions. And we continued our work to develop new uses for the interseeder such as the establishment of food plots for deer and other wildlife.

Our USDA CIG project developed multiyear on farm test sites across Pennsylvania, Maryland and New York. We evaluated several cover crop seed mixes that included ryegrass, clover and a clover vetch mix. In addition we established trials at our research stations to look at different grass species, different legume species and a ryegrass variety trial, which evaluated a range of commercial annual ryegrasses. At our Rock Springs location, establishment was exceptional, likely due to the new design and good growing conditions in June. Establishment at all of our New York locations was exceptional as well. We also gained more experience this year with pre-emergent corn herbicides and are developing some recommendations for achieving early season weed control with minimal impact on the interseedings.

We encountered several issues in 2013 studies. We found that seeding too deep or in soils that are too wet can impact establishment. At our Maryland locations, shading from tall corn was too severe for the cover crop seedlings to survive. At one of our Lancaster locations,nightcrawlers devoured some well established cover crops by early August. Our thoughts are that perhaps earlier seedlings, at the V3-4 stage might create more vigorous cover crops thatcan tolerate some of these midseason stress factors. There could also be alternative species that can better tolerate the shade than those we are using.

At many of our sites, the cover crops tolerated the shade well and have great stands at harvest. The sites in northern PA, New York and Vermont all had very good cover crops. This site on a grazing oriented dairy in Potter County has good ryegrass and should be able to provide some late season forage following an early October silage harvest.

Another producer in Clarion County successfully established a radish/ryegrass mix with an interseeder. We have also had success again this year with the interseeder in establishing legumes and brassicas in existing sods for use as wildlife food plots. The ability to seed, apply N, band apply herbicide and no-till make it a unique tool for this application.

As we continue to gain more experience with the interseeder, we think it has real potential to expand cover cropping into more northern regions and provide all of the benefits of cover cropping to these operations with a modest investment. Our goal is to consistently establish cover crops, while spraying and sidedressing fields, using modest seeding rates of species that will supply N, improve soil quality or provide late season grazing for the crop producer. If you are interested in learning.

Prepared by Greg W. Roth, William S. Curran, Corey Dillon, Christian Houser and Ron J. Hoover, Department of Plant Sciences and Steven Mirsky, USDA-ARS.

In 2012 we conducted another series of on farm demonstration and research trials to assess the potential of inter-seeding cover crops in standing corn.

This complemented some of the research sites established on our research farm and were designed to gain experience with the technology under a broader range of field conditions. The demonstration projects were located in Crawford and Erie Counties in NW PA, in Bradford and Sullivan Counties in NE PA, and in Centre County in central PA.

The cover crops that were interseeded at most locations included Italian ryegrass and a mix of Italian ryegrass and clovers developed for us by a private seed company that we refer to as the Penn State mix. At several of the locations, we evaluated annual ryegrass and other species as well.

In general, weather conditions in the region consisted of a dry period from mid-June through mid-July with minimal precipitation at most locations, followed by good rainfall in late July, early August and early September. This resulted in stress full conditions for cover crop establishment but good conditions for cover crop growth in early September.

A brief synopsis of the farms and research projects is discussed below using the names of the farms as the site location.

Erie/Crawford County Demonstrations

We conducted two trials in Northwest PA with Bob Buhl in Erie County and Stephen Woods in Crawford County, in conjunction with extension educator Joel Hunter.

At the Erie County site conditions were dry for most of the season which is unusual for Erie County. Under these conditions, the mixes seeded with Crimson Clover seemed to persist well, while the grass establishment was very limited. At this site we had some difficulty penetrating the hard soil with the coulter without water in the tank of the interseeder. We filled the tank with water and then achieved good penetration.

At the Woods farm, we compared annual ryegrass to an Italian ryegrass/Crimson Clover blend. Here the grasses established well but the clover did not. At this farm, we found that planting into a manured rye cover crop residue made for a good seedbed for the cover crop, so this could be a long term goal. This field had long straight rows that were easy to interseed in as well. When we returned to the field in mid-October the ryegrass seeded strips were easy to identify.

Figure 1. Crimson clover establishment in early October at the Buhl farm.

Figure 2. Ryegrass establishment in early October at the Woods farm in Crawford County

Bradford/Sullivan County Research and Demonstrations

We conducted two trials in Northeast PA in Bradford and Sullivan County, in conjunction with extension educator Mark Madden.

On the Ron Kittle farm in Bradford County, a relatively dry summer limited establishment of both ryegrasses and clover. At this site, a short residual herbicide program using Resolve gave good season long weed control in corn following alfalfa, which will be useful for future work. This field was part of our NESARE project where we compared a seed coating called 'Yellowjacket' to uncoated Italian ryegrasses and also a Italian ryegrass/clover mix. We did not find a significant effect from the 'Yellowjacket' seed treatment on establishment. Establishment of the Italian ryegrass was spotty, averaging about 2 plants/sq ft. across the field. There was variation across the field in establishment with some areas good and some sparse. In the clover/Italian ryegrass blend at this site, we saw low establishment of the clovers. The border rows here were planted to an annual ryegrass and these seemed to have much better establishment.

On the Wes Hottenstein farm in Sullivan County, we conducted a demonstration in conjunction with T.A. Seeds and Cover Crop Solutions with a variety of species, including oats, ryegrass, and tillage radish. We had success with a number of species, including tillage radish. This field was a high residue no-till field that was planted later in May. This field had a lower plant population than the Bradford site which could have contributed to the better establishment.

The ryegrass/clover blend established well as did the tillage radish and tillage radish/oat blend. The tillage radish here did not develop the large taproots as is typical in some other environments.

Figure 3. At the Kittle farm in Bradford County, establishment was slow and somewhat variable but there was good recovery in the fall.

Figure 4. An example of the radish establishment on the Hottenstein farm.

Centre County Research and Demonstrations

In Centre County, we had two SARE trials where we evaluated the potential of a seed treatment called "Yellow Jacket" on the establishment of an Italian Ryegrass and the Italian Ryegrass/Clover blend.

One was on the Corl farm near Pine Grove Mills and the second was on the Dan King farm near Milheim. At both of these sites, we also did not see an improvement with the seed treatment. Our conclusions are that we were not able to improve establishment with the seed treatment.

Establishment at both of these sites was variable in the field. In some areas of the field establishment was good while in others it was spotty. We also observed little clover in either field. We also did not see any of the sweet clover in either field. This was added to the mix to provide some potential hard seed that might germinate late in the year. During the late summer and fall, we had good recovery of the grass where had some establishment. At both of the farms we saw better stands in the border areas seeded to annual ryegrass. At the Corl farm, they were able to graze cattle on the ryegrass following corn harvest in mid-November.

Figure 5. Following harvest cattle grazed the established ryegrass at the Corl Farm.

Figure 6. Establishment was variable at the King Farm, but fall growth was good in some areas.

Potential Economic Benefits

During this year, we also began to realize the economic potential for a system with interseeding every year in continuous corn.

If an interseeded grass/clover crop could be terminated before planting corn and supply 50 pounds of N per acre and boost cost yields by 7% or 10 bushels per acre, then this could result in a benefit of $35/acre for the N and $70/acre for the additional yield at current prices. If two of the trips for sidedressing ($10/acre), spraying ($10/acre) or no-till cover crop seeding ($19/acre) could be eliminated for one trip with the interseeder ($25/acre) then this would result in an additional $14/acre savings. If realized, these benefits could total $119/acre with an interseeder-based corn cropping system. In some years, forage could be grazed and this would result in additional income. And at the same time, the field would have reduced erosion and runoff and more food for soil organisms and wildlife.


At several sites we had less than ideal establishment this year, but we did learn that there are some strategies that we could add that might increase the success rate under stressful conditions.

Because of the economic and environmental potential, we will be continuing to evaluate strategies for using the interseeder in the future. In 2013 we will be evaluating increased seeding rates, alternative species and varieties, and timing of establishment to improve success. We have also surveyed our cooperators for ideas on modifications to the interseeder to improve performance. If you are interested in learning more about the interseeder, contact Greg Roth at

Partial funding for the work reported here was provided by the USDA Sustainable Agriculture Research and Education Program.

Prepared by: Greg W. Roth, William S. Curran, Corey Dillon, Christian Houser and W.S Harkcom, Department of Plant Science.

The results of the 2011 season using the interseeder. Different ratios of a clover and ryegrass blends were used on different field terrains to test the versatility of the machine. This study was an herbicide application timing study to determine how effective glyphosate is on the weed population.

Penn State Southeast Research and Extension Center, Lancaster County, PA.

This study was an herbicide application timing study to determine how effective glyphosate is on the weed population.

This location was interseeded into standing corn on June 16, 2011. The Penn State mix was planted at a rate of 12 lb/acre and the plots were side-dressed with nitrogen and sprayed with glyphosate.

The corn was harvested for grain in early October 2011. In this field there was a fair to good establishment of crimson clover. Ryegrass growth on the edge of the field was very good, but was reduced under the corn canopy. One lesson learned on this site is that crimson clover can persist through the summer in some situations where ryegrass establishment may be limited.

Figure 1. Growth of ryegrass on the edge of the field

Field Located in Juniata County, PA

The purpose of this study was an interseeding demonstration plot to assess various clover and radish species.

This site is a dairy farm where crimson clover was interseeded at a rate of 12 lbs/ acre into standing corn.

Crops were interseeded on July 1, 2011 along with an Nitrogen side-dressing and glyphosate application. This corn was harvested for grain in mid-October 2011.

In this field there was a fair to good establishment of crimson clover but limited establishment of the other crops. Dry matter yields of 1516 lbs/acre of crimson clover was measured. This was another environment where the crimson clover appeared to establish where some other species were limited.

Figure 2. There was a good establishment of clover but low establishment of other crops.

Centre County, PA, Field Location #1

On this farm, annual ryegrass and the Penn State mix were interseeded to demonstrate the potential fall and winter grazing of dairy cows.

The site is in a riparian buffer zone near a creek. This site was interseeded into standing corn on July 6, 2011 with side dressing and a glyphosate application. The seeding rates for annual rye grass was 20 lbs/acre and 12 and 24 lbs/acre of the Penn State mix.

The corn was partially harvested for silage in early October and the remainder as ear corn. This field had an excellent establishment of ryegrass with some crimson clover. There were plans to use this land for grazing cattle in the fall. It was noted that the cover crop was attracting deer to graze on the clover prior to corn harvest. Dry matter yields averaged 2051 lbs/acre for annual ryegrass and 2489 lbs/acre for the Penn State mix.

The lesson from this demonstration was that in some fields where planting was delayed and no cover crops would be feasible, it may be possible to establish a functional cover crop with interseeding that provides erosion control, nutrient uptake, feed production and wildlife benefits.

Figure 3. The interseeder was used on a riparian buffer zone near a creek.

Centre County, PA, Field Location #2

This was a farm in where annual ryegrass and the Penn State mix were interseeded for the purpose of fall or winter grazing.

The seeding rates at this farm were the same as the previous Centre county location. Interseeding took place into standing corn on July 6, 2011 along with side-dressing and a glyphosate application. The corn height was 24-30 inches tall at the time of seeding and application.

In this field, the ryegrass germinated immediately and became well established. Ryegrass growth was excellent under the corn canopy. The corn at this site was harvest in mid-November as ear corn and averaged 153 bu/acre. The interseeded ryegrass produced dry matter yields averaging 2026 lbs/acre. The owner of this location grazed mules on this field following corn harvest. This was a good example of how an interseeded plot could provide significant fall grazing following a corn crop.

Figure 4. Interseeded cover crops from this farm were used for grazing.

Centre County, PA, Field Location #3

On this farm several species of cover crops were investigated for interseeding, including birdsfoot trefoil, ryegrass, the Penn State mix, and tillage radish.

This farm experienced severe drought and corn yields averaged about 70 bu/acre. Establishment of some of the crops was fair and limited by the drought in the summer, but growth continued through the fall and resulted in fair to good stands in the fall for some species such as the ryegrass and the tillage radish. This was our only use of tillage radish in an interseeded plot.

Field Located in Ephrata, PA

This farm site was another interseeding demonstration site with the purpose of preventing soil erosion on a sloping hillside.

The operator was interested in minimizing runoff on one of their sloping fields with interseeded cover crops. This site was interseeded with several different clover species. The interseeding into standing corn was conducted on June 24, 2011 with side-dressing and a glyphosate application.

Although there was a successful establishment at this site, no matter data was collected. This field had glyphosate resistant horseweed. After treating this field, it was realized that in some cases other post-emergent directed herbicides could be more effective than glyphosate and the interseeder could provide a post direct application of those materials.

Figure 5. Cover crops were interseeded on a sloping hill.